The present invention relates to a device for non-contact transporting and holding of touch-sensitive objects or material.
Several technologies for non-contact transporting of flat objects such as structural elements, vessels or material along a transporting path or holding them in a defined position are known from prior art. For example, transport accessory equipments operated on an air cushion are widely used, wherein the air cushion is generated by a majority of air nozzles. However, these so-called air bearings comprise several disadvantages. Air or any other gas is constantly blown through the nozzles, that is, air or gas is consumed. Often, the air to be used must be cleaned beforehand so that additional expenses arise. Furthermore, air bearings are relatively sluggish with regard to their controllability and whirl up particles, which is not wanted for clean-room applications.
On principle, these disadvantages can be avoided by utilizing other technologies. A transporting device working on the principle of sound pressure is known from patent document U.S. Pat. No. 5,810,155. In this document, a transporting path whit an oscillation generator coupled thereto is described. The transporting path is energized to oscillate so that flat structural elements transferred onto it are levitated by the generated air cushion and do not contact the transporting path at any time. The technology of generating stationary waves, which merely effect that a structural element is levitating, is well known. Furthermore, technologies of generating moving waves, which effect that a structural element is moved along the transporting path, are also known.
Another constructions according to the prior art are described in the documents DE 19916922, DE 19916923, DE 19916859 and DE 19916872.
The devices of this kind so far described, which were used under laboratory conditions only, show that it is possible, on principle, to transport or hold a structural element on an oscillating transporting path in a non-contact way.
However, with trials carried out in practice by using such a device, considerable problems arose when the structural elements to be transported were more weighty than thin silicon wafers or similar light-weight materials, for example, which will be described as follows: The transporting path has a certain specific gravity and specific oscillating properties. When the transporting path is operated in the idle motion, that is, when no structural elements are levitating on it, the oscillatory response thereof can be calculated exactly. However, when the transporting path is differently stressed by the structural elements to be transported, the resonant conditions, and thus, the oscillatory response thereof will change permanently. This can lead to the fact that, at certain sections of the transporting path, the air cushion generated is not sufficiently thick so that the structural elements can contact the transporting path. In order to reliably prevent the transporting path from being contacted by the structural elements, the transporting path and the oscillation generator must be dimensioned so that the former is always oscillating sufficiently strong at all sections of the transporting path, even if exposed to greater stresses. However, this causes stronger oscillation generators to be used, with the result, that the equipment cost and also the cost of energy increase.
It has turned out that construction and operation of transporting devices according to the principle just described will be too costly and expensive when large-surface and more weighty structural elements such as glass plates in a size of one square meter, for example, have to be transported. In such a case, it would be necessary to arrange many oscillation generators beneath the transporting path, in series and, if need be, also in parallel. However, this would lead to remarkably higher first cost. Another problem is that the oscillation generators have to be adjusted to each other correctly in order to gain the wanted optimum oscillatory response of the transporting path. As the oscillation generators themselves are subjected to a certain aging process causing the oscillatory response thereof to be changed slightly, the oscillatory response of the transporting path must be readjusted by using a suitable automatic control. Such a control is only possible when the vibrations of the transporting path are measured continuously, so that because of the extremely high technical expenditure, this technology did not prevail.